Urban hotspots
China’s megacities are sizzling, revealing a future many more of us will face – and also some ways to cope, finds You Xiaoying
 Humidity makes Shanghai’s heat more unbearable
LUKYEEE1976/GETTY IMAGES“MY OFFICE felt like a steamer on Monday morning,” wrote Chinese influencer Bi Dao in a social media post in August. He fetched a drink from a supposed cold-water dispenser – it was 40.8°C (105°F). Bi, who lives in Hangzhou, a regional capital on China’s east coast, decided to roam the city with a temperature gun, pointing it at things to find out exactly how hot they had got. “The ground was 72.6°C, the seat of a sharing bike was 56.5°C, the handrail in the metro station was 45°C, even the tree bark was 38.7°C,” he wrote. He ended his post by thanking Willis Carrier for inventing the air conditioner.
Hangzhou is known for its beautiful lake, large pagoda and rolling green tea farms – not for heat. But what Bi witnessed was only one of the 60 “high-temperature days” – ones that topped 35°C (95°F) – that grilled the city and its 12.5 million inhabitants this year. Hangzhou isn’t alone. Many cities worldwide are feeling the heat. Things are getting so bad that growing numbers of people face temperatures that are beyond human endurance.
Already, such conditions kill around half a million each year. That will inevitably rise as climate change increases the number and intensity of heatwaves around the globe. Cities are on the front line of this unfolding crisis. And China’s vast, densely packed megacities are leading the way. As well as providing a glimpse of what we are in for, they offer lessons that could help urbanites everywhere adapt, from their “vertical forest cities” to cleverly designed parks – and new, cool building materials.
Many temperature records have been broken this year, with astonishing readings reported worldwide, from Perth in Australia to New Delhi in India. This isn’t a flash in the pan. The probability of heat extremes has nearly doubled every 10 years since 1979. And things are getting worse. “In the past decade or so, there has been a tremendous increase in intensity and frequency of heat extremes,” says Robert Vautard, who co-chairs a working group at the Intergovernmental Panel on Climate Change. The past northern summer was the hottest on record, with average temperatures between June and August 0.69°C higher than the 1991 to 2020 average for those months. It beat the previous record, set just last year, prompting UN Secretary-General António Guterres to comment that “the era of global boiling has arrived”.
According to research published last year, if current climate policies continue, a third of the world’s population will live outside of a safe temperature range by the end of this century. The study looked at the “human climate niche” – the temperature range most suitable for our survival (see “Deadly heat”, page 38). “We project that every 0.1°C of further global warming will expose around 100 million people to extreme heat risks. That is a major concern,” says one of the researchers, Tim Lenton at the University of Exeter, UK.
Urbanites will bear the brunt because cities suffer what is known as the urban heat island effect. This is a result of having less vegetation – which can counter heat – than rural areas and many buildings, pavements and roads that absorb sunlight and radiate heat. “The experience of heat in cities is very different from heat in the countryside,” says Eric Mackres at the World Resources Institute’s cities programme. “Think about the way it feels to stand on a hot, unshaded pavement with no breeze and the sun beating down on you.”
Cities are already home to over half of us and by 2050 nearly 7 in 10 people are projected to be urbanites. This exodus from the countryside is especially pronounced in China, where the shift to city dwelling has exposed an extra 115 million people to extreme heat over the past two decades. By mid-century, the population experiencing heatwaves there is projected to jump by as much as 12-fold.
To put things into context, the Yangtze River Delta region in the east of China, which includes the enormous cities of Hangzhou, Shanghai and Nanjing, is now one of the world’s largest urban clusters. One-and-a-half times the size of the UK and home to 220 million people, this region baked in record-breaking heat for more than two weeks straight from the end of July this year, earning it the nickname China’s “oven”. Summers also happen to be humid in many of the nation’s economic hubs – including Shanghai, Chongqing and Hong Kong – due to the monsoon climate. Humidity compounds extreme temperatures because it becomes harder for people to sweat.
Record-breaking summerAcross China, this past summer was a taster of what is to come. Relentless waves of extreme weather scorched many places for weeks on end, leading to a barrage of heat warnings and broken records. July was the hottest month ever seen in China. But as early as mid-June, temperatures in the capital, Beijing, were already pushing 40°C (104°F). Crossing the city’s notoriously wide roads in the sun became a physically demanding mission, even for the young and healthy. Iron-willed tourists on Tiananmen Square equipped themselves with sunglasses, parasols and anti-UV face masks as they admired the country’s political heart in the heat of the day. Increasingly, people wear portable air conditioners around their necks.
“Frequent extreme heatwaves have arrived earlier than we had expected, and their intensity is getting stronger and stronger every year,” says Xu Chi at Nanjing University. Summers are also lasting longer. On 22 August this year – a day that should have been chu shu, meaning “the end of heat”, according to China’s traditional season calendar – another regional capital, Chengdu, issued a red alert for a heatwave. During the week to follow, the city of 21 million in the south-west experienced power shortages due to surging electricity demand driven by the use of air conditioners.
In China and beyond, exposure to excessive urban heat is, in many ways, an issue of social justice. Vulnerable groups ranging from low-income communities to the elderly are expected to be disproportionately affected. For example, those who toil outdoors will probably lose significant working hours as extreme heat becomes more and more frequent. “The same heatwave is not the same for all people, such as those with pre-existing conditions or living in certain types of buildings or maybe buildings without air conditioning,” says Weng Qihao at the Hong Kong Polytechnic University. And, globally, the countries most affected by extreme heat are often those with lower and middle incomes: research indicates that the five with the highest numbers of people at risk of exposure are India, Nigeria, Indonesia, the Philippines and Pakistan.
Yet, we have been slow to react to the growing threat, perhaps because heat is an invisible killer. The first thing cities should do, according to Vautard, is “prepare for temperatures that are much higher than current extreme ones”. For Wang Yujia at the University of Nebraska-Lincoln, a crucial aspect of this is to improve the outdoor environment. “There’s a big difference between a city being survivable and a city being livable,” he says. “The question is how do we make sure that, in the face of the rising heat, we still maintain the same quality of living where people, especially children, can go out there and enjoy their time in the outdoors.”
“Exposure to urban heat is, in many ways, an issue of social justice” Tourists braving the heat in Beijing’s Tiananmen Square
WANG YUELING/XINHUA/ALAMYOne answer is trees. Research shows that they can cool the surface temperature of cities by up to 12°C (22°F). And creating urban forests within 1 kilometre of residential areas is the most effective way to reduce heat-related deaths, according to a new study by Song Jinglu at Xi’an Jiaotong-Liverpool University in Suzhou, China, and her colleagues. She hopes this finding will guide planners in compact cities to identify suitable spots for such planting.
Trees are already being used to remarkable effect in Nanchang, an industrial city and the capital of the landlocked Jiangxi province in south-east China. Its Fish Tail Park is a 51-hectare wetland featuring dozens of wooded islands on a lake. Completed in 2021, it was built by a team led by Yu Kongjian, the brains behind “sponge cities” that can mitigate excess water, as part of the national flood-control programme. It has since become a go-to place for the city’s 6.2 million residents seeking refuge in its notoriously humid summers.
There is good reason for the park’s popularity. Average temperatures on its forested islands are between 2 and 4.6 per cent cooler than in the surrounding streets. “It’s a unique piece of urban ecological park,” says Wang, who made these measurements with his colleagues in summer 2023. Because it was built as a sponge city park, its elevation is lower than the surrounding urban areas, a feature that doesn’t just let water drain away, but also allows cooler air to circulate. “You get lower temperature and increased wind,” says Wang.
Going greenerOther Chinese cities have adopted a variety of initiatives to boost their greenery. Shenzhen, a city of more than 17 million in the south, for example, is promoting plant-abundant “green roofs”. These can lower ambient urban temperatures by around 1°C (2°F) and slash the electricity demand associated with cooling by 8 per cent. And in the province of Guangxi in southern China, a “vertical forest city” is being built in Liuzhou, featuring high-rise blocks planted with thousands of trees and shrubs.
Increasing urban green spaces is a “highly effective way” for cities to adapt to extreme heat, says Lenton. It has the added benefits of offsetting carbon emissions and improving well-being. And it is relatively cheap. “There needs to be targeted investment in increasing green space in the global south and especially the poorer parts of cities,” he says.
When it comes to cooling indoor spaces, there is another cheap, low-tech solution: “cool roofs” – ones painted white or covered with certain materials, such as light-coloured gravel, to reflect sunlight. “There’s no real cost to it because the materials used for traditional cool roofs are no more expensive than a typical roof,” says Aaswath Raman at the University of California, Los Angeles. But the benefits are substantial. A cool roof can lower temperatures inside a home lacking air conditioning by up to 3.3°C (6°F). In one with air conditioning, it can reduce the amount of cooling needed to keep the space at a comfortable temperature by between 11 and 27 per cent. This is a double positive because air conditioners belch waste heat into the outside air, making cities around 20 per cent hotter during heatwaves, and they are also responsible for around 20 per cent of the total electricity used in buildings worldwide. Demand for air conditioning is expected to more than triple by 2050, a big worry given that burning fossil fuels is still the primary means to generate power.
“We have been slow to react, perhaps because heat is an invisible killer” A vertical forest city block.
STEFANO BOERI ARCHITETTI Trees in Fish Tail Park
TURENSCAPE“Unless all the energy driving air conditioning is clean, you’re going to have this feedback loop. Hotter temperatures mean more air conditioner use, which means more carbon emissions,” says Raman. He and his colleagues are attempting to curb this vicious circle – and provide ways to make indoor spaces more comfortable for people who can’t afford air conditioning – by developing materials that can cool buildings without using electricity. It began a decade ago, with the invention of a multi-layer material that remains cold even in direct sunlight because it radiates heat at a wavelength that can escape straight into space without being captured by the atmosphere. Since then, Raman has co-founded a company called SkyCool Systems to develop a series of other cooling materials. These include a film that can be applied to roofs and outdoor structures and a panel that improves the efficiency of refrigerators.
Raman believes a lot can be done to buildings and outdoor spaces to combat heatwaves – for example, creating cold surfaces near people waiting for a bus. “We are thinking about how this could be used in lower-income countries that don’t have good insulation in a lot of buildings,” he says. He has even found that a layer of metallised polypropylene would help windows and walls reflect more heat – it is the stuff used to make crisp packets. “You could imagine retrofitting facades with recycled potato chip bags,” he says.
Other experts say what is needed most – at least in the short term – are administrative measures to deal with excessive heat. “This can involve immediate actions during a heatwave like rescheduling school and work hours or setting up areas where the public can access drinking water, escape the heat and, if necessary, get medical attention,” says Clair Barnes at Imperial College London.
Authorities in Hangzhou are clearly aware of this. In August, as the heat became unbearable, the city’s government opened cool, underground air-raid shelters, capable of holding thousands of people, providing free cold tea, Wi-Fi and ping-pong tables. Apparently, the measure proved to be a hit.
 You Xiaoying is a freelance climate writer based in London¦ |
